1. Field of the Invention
The present invention is generally related to marine propulsion systems and, more specifically, to a heat shield provided for an elastomeric sealing component to prevent heat damage from being caused to the elastomeric component by a exhaust gases.
2. Description of the Prior Art
Many different types of marine propulsion systems are well known to those skilled in the art, including outboard motors and stern drive units. In certain types of marine propulsion systems, exhaust gases from an internal combustion engine are routed through a propeller hub of the propulsion system. It is also generally known to those skilled in the art that elastomeric seals are particularly advantageous for sealing a lubrication compartment from the water in which the propulsion system is operated. It is also known to those skilled in the art that certain devices, such as fishline cutters can be provided within a propeller hub or near the elastomeric seals.
U.S. Pat. No. 3,619,083, which issued to Witte on Nov. 9, 1971, discloses a cutter which is mounted on the inner end of the propeller hub of an outboard marine propulsion unit for the purpose of cutting fishlines which become entangled upon the propeller. The fishline cutter also protects the gear case seal from damage by the fishline.
U.S. Pat. No. 3,871,324, which issued to Snyder on Mar. 18, 1975, discloses an outdoor propulsion unit exhaust discharge system. The system is used with an engine driven outboard propulsion unit having a reversible propeller in order to selectively drive the propulsion unit in forward and reverse directions. The device also comprises passage means for conducting the exhaust gases from the engine through the unit. The pair of underwater discharge openings for the propulsion unit are provided and respectively disposed fore and aft of the propeller to provide for selective exhaust discharge into the outflow of the propeller slipstream regardless of the direction of propulsion unit operation. This assures a solid flow of water to the propeller in both forward and reverse directions of operation of the propulsion unit.
U.S. Pat. No. 3,943,790, which issued to Meyer on Mar. 16, 1976, describes a marine outboard gear assembly. The invention includes a marine outboard gear assembly which is usable in an outboard motor or an inboard-outboard drive. It features a constant drive of the meshing gears which transfer power to the propeller shaft axis and selective spring-clutching direct to the propeller shaft. It utilizes the meshing gears for lubricant circulation as long as the engine is operating and whether or not the clutch is engaged. It also reduces to an absolute minimum the drag and inertial effects operative upon the propeller shaft when the boat is moving in the declutched condition, such as when the propeller is windmilling. Also shown in this patent is a particular subassembly of gear and clutch parts on the propeller shaft whereby desired axial clearance can be readily pre-adjusted and selected, prior to assembly of the gear case.
U.S. Pat. No. 3,356,151, which issued to Strang on Dec. 5, 1967, discloses a marine propeller which includes a hub that is adapted for rearwardly discharging exhaust gases and which has, at the rearward end thereof, an annular ring located in adjacently outwardly spaced relation to the propeller hub and cooperating with the propeller hub to provide one or more passageways serving to deflect water flowing rearwardly about the hub into the exhaust gas stream.
U.S. Pat. No. 5,522,703, which issued to Okamoto on Jun. 4, 1996, describes a propulsion system for an outboard drive. The system includes a seal between adjacent ends of a pair of counter-rotating propellers. The seal inhibits fluid flow through a joint between the propellers, while minimizing frictional contact between the counter-rotating propellers. In at least one embodiment, the seal contacts only one of the propellers.
U.S. Pat. No. 3,748,061, which issued to Henrich on Jul. 24, 1973, describes a propeller construction. The propeller includes a bushing part adapted to be mounted on a propeller shaft for common rotary movement of the bushing part with a propeller shaft. A resilient member is bonded to the outer periphery of the bushing and has an outer non-circular configuration including a series of alternate areas of greater and lesser radial distance from the axis of the bushing and a propeller blade part having a hub including a bore with an inner configuration including a series of alternate areas of greater and lesser radial distance from the axis of the propeller and detachably receiving the resilient member.
U.S. Pat. No. 3,246,698, which issued to Kiekhaefer on Apr. 19, 1966, discloses a diffuser-pump for marine propulsion propeller hub exhaust systems. The invention is based on an improvement in known prior structures and generally contemplates the utilization of a removable replaceable combined diffuser-pump member at the extreme discharge end of the hub. More specifically, the member is secured for rotation with the outer end of the propeller shaft and includes radial veins integral with a flared diffuser ring which act in combination to pump water from the hub.
U.S. Pat. No. 5,527,195, which issued to Neisen on Jun. 18, 1996, discloses a flow through marine propeller. The propeller has an integral aft skirt portion with a plurality of slots extending forwardly from the trailing end and dividing the skirt portion into a plurality of circumferentially spaced segments separated from each other at the trailing end by respective slots therebetween and integrally joined to each other at the outer hub forwardly of the slots. Aft trailing blade tips of the propeller blades meet the outer hub at points offset from the slots to prevent engine exhaust in the through hub exhaust passage from seeking the negative pressure backside surfaces of the propeller blades through the slots.
U.S. Pat. No. 5,816,869, which issued to Willows, on Oct. 6, 1998, discloses a propeller for varying the exhaust length. The marine propulsion system provides variable length exhaust paths depending upon the speed of the boat and motor. The propeller includes a propeller hub and an exhaust tube positioned within the propeller hub. The exhaust tube extends past the aft end of the propeller hub and defines a first exhaust passageway. A second exhaust passageway is positioned between the propeller hub and the exhaust tube. The second exhaust passageway is shorter than the first exhaust passageway. At low speeds, engine exhaust exits the longer first passageway, while at moderate speeds, engine exhaust exits the shorter second passageway. As a result, the effective length of the exhaust path varies depending upon the speed of the motor, such that the length of the exhaust path is specifically tuned to several speeds of the motor.
U.S. Pat. No. 4,373,922, which issued to Weed on Feb. 15, 1983, discloses an outboard propulsion gear case. The outboard drive unit for a watercraft has a through-the-propeller hub exhaust system for engine exhaust and has a bearing support member which carries the propeller shaft and separates the exhaust passages from the propeller shaft gears. Lubricant retaining surfaces are formed on the bearing support member to prevent corrosion between the support members and the housing.
U.S. Pat. No. 4,388,070, which issued to Kasschau on Jun. 14, 1983, describes a propeller exhaust hub and shroud. The propeller is intended for controlling the discharge of gases and cooling water exhausting from the central hub of an outboard motor unit comprising a cylindrical shroud surrounding the propeller hub to confine the exhaust to the innermost part of the blades and discharging it downstream of the propeller when operating the unit in the forward or reverse mode. Several attachments to the shroud which enhance the discharge performance of the propeller are also described. An alternate embodiment of this device comprises a shroud which can be attached to a conventional through-hub marine propulsion device to channel the exhaust away from the propeller area.
U.S. Pat. No. 4,511,339, which issued to Kasschau on Apr. 16, 1985, describes an exhaust propeller assembly. The propeller is used for controlling the discharge of engine exhaust gases from the central hub of a boating motor unit by making provision for confining the gases to the inner most fraction of the structure and discharging it downstream of the propeller when operating the unit in either the forward or astern mode of operation.
In marine propulsion systems that provide for the passage of engine exhaust through or near the propeller, hot exhaust gases can possibly be drawn into heat sensitive regions of the unit when the propulsion system is operated. More specifically, hot engine exhaust gases can be drawn back into the propeller hub and, eventually, in thermal communication with elastomeric fields that are used to contain lubrication fluids within the gear case. The heat from the exhaust gases can cause severe damage to the elastomeric portions of the seals. It would therefore be significantly beneficial if a means could be provided for protecting the heat sensitive materials used in the sealing components of marine propulsion systems under these potential damaging conditions.